by Susan Davis, USA TODAY

by Susan Davis, USA TODAY

WASHINGTON - Rep. Joe Walsh, R-Ill., has been outraised by his Democratic opponent, disabled war veteran Tammy Duckworth, for the duration of their race for a suburban Chicago U.S. House seat, but in the homestretch Walsh has leveled the financial playing field with the assist of just one outside group, the Now or Never PAC.

Now or Never PAC has dropped $1.7 million in television ads into the race in two weeks. It is the only U.S. House race the group has invested in this year. The group - whose founders do not have to be disclosed and remain unknown - is part of a burgeoning class of boutique super PACs that target a short list of candidates, and often just one individual race.

"It's amazing that several donors matched us in a couple of weeks," said Anton Becker, a spokesman for Duckworth's campaign. Duckworth is favored by election forecasters to win the district, which was redrawn to favor Democrats in the 2012 redistricting process, but Becker said the campaign is mindful of the potential impact a flood of negative ads could have in the closing weeks.

"This is the super PAC world we live in now," said Justin Roth, a Walsh campaign spokesman, who said the congressman is happy to have the support "of any person or group that believes in his views of smaller government, low taxes and freeing small businesses from burdensome regulations."

Much of the focus of the 2012 election has been on the impact of the new, behemoth super PACs like Crossroads GPS which has said it will invest around $300 million in the presidential and dozens of congressional races this year.

These groups were born out of a Supreme Court decision that ended the long-standing ban on the use of corporate and union money in federal elections. Super PACs can raise unlimited funds, don't have to disclose their organizers but do have to disclose donors, and have run almost entirely negative ad campaigns. They can't coordinate directly with candidates.

The flood of money from Now or Never PAC erased the $1 million fundraising edge Duckworth had over Walsh. "Exactly, that's the whole point," said Tyler Harber, a spokesman for the PAC who would not disclose the people behind the group except to say it was created by "a handful" of businessmen and political operatives who have worked in Washington. "They all have the same interests," he said.

The interest, according to Harber, is to find races on the margins that aren't considered competitive and where other groups aren't playing and try to make them winnable for Republicans. He said there is no agenda behind the PAC beyond electing Republicans.

The only previous race the PAC sought to influence was the Missouri GOP Senate primary, where they unsuccessfully backed Sarah Steelman, who lost to Rep. Todd Akin. The PAC also announced last week it will get in to the Wisconsin Senate race on behalf of former GOP governor Tommy Thompson.

As for Walsh, a conservative who is popular among Tea Party activists, Harber said research, not ideology, guided the group's decision to advertise. "Our research indicated that Tammy Duckworth was and still is vulnerable," he said, "I think in the next four weeks we'll be able to prove that we were able to have a positive effect."

A growing number of congressional candidates are the lone targets of boutique super PACs. For example:

-- America's Road Ahead Fund has targeted just one Democratic candidate, Democrat Christie Vilsack, who is running against Rep. Steve King, R-Iowa. The group has spent $38,000 on a television ad. The group's biggest donor is Frank Brownell, the CEO of an Iowa-based company that sells gun parts.

-- End the Gridlock PAC has spent $1 million on radio and television ads alone against Nebraska Senate Republican candidate Deb Fischer, who is running ahead of former Democratic governor and senator Bob Kerrey. The group is funded by a cadre of wealthy businessmen including Wallace Weitz, the president and founder of Omaha's Weitz Fund, and Los Angeles-based philanthropist Sidney Kimmel.

-- The Texas Conservatives Fund spent $5.5 million this year in an unsuccessful effort to defeat Senate GOP nominee Ted Cruz. It has supported no other candidates since. Donors were supporters of Cruz's primary opponent, Lt. Gov. David Dewhurst.

-- The Committee to Elect an Effective Valley Congressman has spent more than $700,000 on behalf of one lawmaker, California Democratic Rep. Howard Berman, who is in an intra-party general election fight against Rep. Brad Sherman. Donors include Hollywood moguls Jeffrey Katzenberg and Peter Chernin.

-- American Sunrise PAC is targeting Rep. Allen West, R-Fla., in his race against Democratic Patrick Murphy. The PAC's founder and biggest donor is Thomas Murphy, Patrick's father, who has invested at least $250,000.

The success rates of these efforts remain unclear because this is the first election cycle testing their mettle. The groups are troublesome because voters have no way of knowing who is behind them, said Bill Allison, the editorial director of the government watching group Sunlight Foundation which tracks super PAC spending. The PACs are a growing force in campaign finance and a new reality for candidates seeking office.

"Now we have a system where because all of this is perfectly legal and legitimized, it creates this huge opportunity for political consultants and big donors to influence not only presidential and congressional races, but state and local ones as well," Allison said.